There are numerous file formats for storing video data in data files. Video data is commonly compressed according to a compression algorithm to produce a bitstream of compressed video data. Compressed bitstreams are stored in data files that have a specified file format. Thus video data generally has an encoded bitstream format and a file format.
One family of compression algorithms collects images from a sequence of images defining the video data into groups, called a group of pictures. The images in a group of pictures are processed using redundancies among the images in the group of pictures to reduce the amount of data required to represent each image. In general, such compression algorithms compress at least one image using only data within that image spatially, thus using “intraframe” compression. Such images, when compressed, are referred to as I-frames. Other images are compressed using data from other images, and thus such algorithms use “interframe” compression. If those other images occur in the sequence of images both before and after the image being encoded in display order, then the compression is “bidirectional”, and the encoded image is called a “B”-frame. Other images may be compressed using data from other images that occur before the encoded image in display order in the sequence of images. These are commonly called “P”-frames.
Common compression technologies that uses I, P and B frames when compression long groups of pictures in video is MPEG-1, MPEG-2, MPEG-4 Part 2, H.264/AVC, SMPTE VC-1, and the coming HEVC. One in particular, called AVCHD, uses a compressed bitstream in the H.264/AVC coding format, and the encoded bitstream is in the MPEG-2 Transport Stream (M2TS) format. The M2TS format is optimized for streaming playback, such that compressed data for an image might be packetized in several packets, and these packets can be multiplexed in an encoded bitstream with other data, such as compressed audio. Such a file format is commonly used in consumer-grade video cameras that store AVCHD encoded video data into data files.
When video files are later played back or edited, the playback system of either a media player or a video editing system generally allows a user to scrub or seek through the video, for example to find a point of interest. Video data that is encoded without indexing information to some recovery pictures generally adds complexity to such a playback or editing system.